SOLVED - '04 gauges out, rev light out blowing fuse #21
 

Rev. light, blinkers, A/C, moonroof, PW all out, fuse blew again fast when in gear...
'04 Honda Accord EX, AT, 4 cyl. 90K. Been great except for pass door lock actuator (been out 2+ yrs)...

Hi all, new here. Very active member of other moto forum.

Other day, powered up car at night and noticed gauges out. Then more. Car locks AT in park, have to bypass it by pressing down shifter release under that pop out tab on Trans.
PW won't work at all, P Moonroof out too. Reverse lights out, don't come on. No blinkers, although the Hazard button will activate them all just not on the stalk. A/C not working either - no cold air and was working before. (no odometer, no gas gauge, no speedo, and we're still driving it daily).

Checked and fuse #21 blown "IG Meter" 7.5 amp. Borrowed "IG Wiper" 7.5 amp and got everything working immediately with new fuse car off, started car, still good, and either right after I hit the brakes or maybe 30 feet up the road gauges black out, blown same fuse, all same still not working again.

Checked around trunk for any wiring being severed (no electric work done on car, nothing added recently - car is completely stock). Pulled brake light bulbs. Passenger side brake light bulb not working. Swapped driver side brake bulb to pass side brake and then it worked, although it seemed to heat up pretty fast in my hand compared to working driver side... and it went from clear and darkened in a matter of minutes...
But brake lights (besides blown pass bulb) have always been working, radio fine, heated seats, climate control and fans, interior lights, headlights, P mirrors, P Seat, all work fine.

Any suggestions? I have a solid DVM but I don't have any real experience in tracing and fixing shorts. Also have 6-24 Volt bulb testors etc etc...

progress...! AND how to
 

So hooked up a little test light with leads into my #21 empty fuse slot.
Went through whole circuit, the test light connects the circuit but won't blow (like a fuse will) and enables to pinpoint where the problem is.

Here's how this works,
Connected test light (which happens to be one rated for 6V - 24V) glows dim if there is not a problem or something that will blow normal fuse (short drawing too much juice).
BUT light will glow very bright when you've detected the bad area. (You can also rig this up with, say, a headlight bulb, tail light bulb etc... but be very careful to not connect two extension leads together when inserting them into either side of fuse block).

So in this case:
Wipers - working - normal dim glow
all 4 Power windows - working - normal dim glow
Power moon roof - working - normal dim glow
blinkers both - working - normal dim glow
reverse - working - normal dim glow

WHEN car (AT) is in 'Park' and I hit the brake pedal to shift - HA - light glows very bright and hear a little click!
When I shift into gear, and even reverse, neutral, D etc... I can hit the brake and it's fine, it's very specifically when car is in 'Park' and I hit the brake I am exposing the short in the system.

I read somewhere else that Honda's brake pedal switch aka brake light switch is somewhat notorious for going out.
Just bought replacement one for $10 at local O'Reilly's and will post later with results.

Hmm. Brake pedal switch I don't think is it. Tried new one and old one same results.
With test light in to complete circuit I can get everything on the car to work except I cannot shift out of park without manually pressing in override next to shift handle.
Perhaps the circuit being one way or other with brake switch made the light glow get brighter and didn't indicate the short was there.

But maybe for awhile before this all happened?? I have pass side brake light out although bulb looks fine it won't work in socket. And I have both reverse lights bulbs with broken filaments which I don't know if its related or a crazy coincidence.
Anyone?

Remove the reverse light bulbs and test again.

Ok, I did remove the reverse light last night. I will try re-testing it again now.
Thank you for the response Poorman!!

(could blown reverse lamps cause that fuse to blow and all this?? Is this a sort of 'safety' built in mechanism to tell the dumb driver both reverse or say all 3 brake lights are out, and by golly, the car is going to get the dumb driver's attention!?)

There is a fuse #7 for back up lights according to manual and fuse box cover. that fuse is not blown. I think it's a coincidence but will keep trying.

i just posted a six minute response to all this, very detailed and this p.o.s. site just timed me out with it's 'token' and wiped out my whole text. thanks for the constant ads too, those are really helpful.

The car blows fuse #21 any time for a split second AT goes into or through Reverse.
AT shift lock solenoid is working, I can hear it click loudly at AT console cover when I have a new fuse in #21 and haven't done anything involving reverse yet. It will also let me shift out of park with brake on like it's supposed to but if I go as far as Reverse BAM! fuse instantly gone. (like ACC key position or running in neutral or and other gear or park I have everything working and can shift gears etc..). I can hit brakes in any gear, no problem. Brake light always work and replaced brake switch and original wasn't faulty.

I traced two solid green with painted on grey spots as both the + 12V to both reverse light bulbs with black grounds. The greens I traced to upped shoulder rear passenger side connectors when I took out the leather side trim seatback bolster. I disconnected the connector there, and still blow #21. I had also put in new reverse bulb to test with same problem before I disconnected. So I know it's not bulb related in rear, nor is it have anything to do with final wiring from connector on into trunk and fixtures. I traced the larger wire loom down through both door sill covers, no obvious breaks or tears in loom or anything shorting outside of plastic to body.
I have a lot of the driver footwell plastics out when I did the brake switch and see there are TONS of green and grey painted dot wires in there to a dozen plus connectors. Nice. Anyone have an idea which to disconnect for testing etc...?
I have Digi Voltmeter and test alligator auto bulb things so where should I look now???

The wire color protected by the 7.5 amp fuse #21 is yellow.

It powers a bunch of different items that you listed previously.

The gauge control module is one of those items that is powered by the yel wire. There is a self-diagnostic test that you can try.

Push and hold trip/reset button
turn headlights on
Turn ignition switch on
Within 5 seconds, turn headlights OFF, then ON, then OFF.
Within 5 seconds, release the trip/reset button, then push/releas the trip/reset button 3 times repeatedly.

The car will test several items and you will hear beeps, etc.

What you will pay attention to is the mileage. If it says 88888888, then no problems were found. If a problem is found, it will read Error 1, Error 2,...

I know it sounds like a strange diagnostic, but I have tried this on my TSX and it works.

Let us know what you find.

Sounds like OBDII stuff... had my fun with that on junk Supra...
Will try that,

also wondering where the grounds are for this circuit, and if there's a wiring diagram available to see anywhere

Thinking it could be trans reverse switch on the actual transmission or the wiring from it, did a fast visual look tonight and think I spotted it and no visual tears etc... but in daylight will probably pull that connector and see what that does as well.

Other things it could be?

Just found this diagram for slightly older accords. May swap ignition relay for back up relay at fuse box area tomorrow and see if #21 fuse still blows.
Cannot locate any individual grounds in trunk area either. Where are they?

Here is what I have for the underdash fuse panel.

Here is a backup light circuit for your '04

Thanks for the diagrams Poorman!!
It looks like if I read it right, on my AT car, the relay is upstream and could not blow the #21 fuse. Also I gather I don't have a Back Up Light switch on the actual transmission in the engine bay - that's only for MT? So my sending unit is probably below that center console. But the AT shifts into all gears fine as long as fuse #21 is good, or I use manual shift lock override, so i don't think it's the transmission range switch. The gears were indicated fine on the gauge and on the shifter as it went into gear...

I thought I smelled a little burning smell the other day and saw a wisp of smoke very slight at night in the headlights coming in front of car, from roughly where the AT would be - this was during and after I had been using my 6-24 V test bulb to connect the #21 fuse and test the PW, Moon roof, blinkers etc... for several minutes. Could be nothing. But had me thinking it was some sort of Reverse switch wiring going up in smoke. Any thoughts on that? Is there anything like that out in front on the Transmission?

I may switch the IG relay and Back up relay mostly for my amusement today, but I think again, that it can't be blowing the fuse :(

The "reverse" switch is in trans range switch which is on the side of the trans.

Also found this in a Mitchell pdf shift interlock diagnostic:

Poorman you tha man! Thanks!. Going out with my ipad now to go mobile with your diagrams.

Just snapped pic of my owners manual sold with car. Look at #7 description. Honda idiots.

I just swapped the ignition relay with the reverse relay marked "ACC" in my car. Same thing. the Reverse relay will work and allow me to start car. (no relay in that spot I can't start car so that's how I know both are working).

I've been all over the engine bay from top and from the bottom as well. I cannot find any lengthwise front to back long connector on the side of my Auto Trans. I can see about 13 other connectors of course none of which I have any clue what they are.

Anyone had experience with this connector and can give a more descriptive way to find it? I assume that diagram is Down = front, Up = back of transmission from a bird's eye view looking straight down on the Auto Transmission.

Hell, what if I just pull the reverse relay altogether out? It IS listed as ACC so does that mean I lose a lot of stuff OR only just the reverse lights and the AT dash board indicator status of what gear car is in? According to the wiring diagram that might be it.
At least for now, I might live with that. It's been over two weeks here like this, and I think I also read having #21 fuse circuit down also means I have no radiator fan??? Is this true? If so I could overheat my car in CA summer heat - not good.

Attached is a picture of the transmission range switch. You have to remove the cover to see the connector and more of the wiring.

You may have a short there.

Thanks! I did see that unit and thought that was the range switch. So I think there is a separate connector towards the front of the car that sends something to it? Maybe not and I am confused.
So I could probably figure out a way to get cover off, but I'm working on the city street so to speak... and then is there an actual switch I can pull out and test?

I have a multimeter but my ohm-ing apparently sucks as I've gotten strange readings on other things and verified things were good when they weren't and vice versa. Specifically resistance testing only. Voltage metering I'm just fine at.

I think it was the transmission switch harness connector that I disconnected down low in the front of the car on the AT, wondering if I leave this disconnected, OR the 'ACC' relay which may only operate the reverse lights or it may do a whole lot more. I guess it doesn't make a lot of sense a relay would do anything useful to operate a radio, moon roof, windows etc etc... now that I think about it.
Maybe I'll test both on my last 2 fuses and see what happens.

Attached is the connector I am pretty sure I pulled earlier today. Found a how to diagnose for an older honda civic but it looks the same...

That didn't work.

Pulled back out 'ACC relay' aka the reverse light relay and everything in the car worked just fine with new #21 fuse in. Gears all shift fine. AND the dashboard gear selector works for all the gears N D D3 2 1
notice I didn't say R. As soon as shifter selector went into R you've seen this movie before - bam! - out goes fuse #21 yet again.

Also, had wrong connector out and car could not drive. Re-hooked mystery front lower connector back and car can drive again.

This is getting more than a little tiring. Good part of 3 days on this online and in the car and only verified that certain parts work and nothing solved.

One thing though, since car Transmission will hit all the gears and work, the shift indicator works, and the dashboard gauges shift indicator all work correctly (can't verify R works in dashboard since it instantly takes out my whole dash, and I remember P worked right on dash pre blown fuse), I would think that my Transmission Range Switch is working correctly simply based on that alone.
Is the only possibility left there is the wire to reverse that is shorting somewhere under the hood or near fusebox area? Thank you for any wisdom sent this way previously and in the future.

PAhonda:
I got the self diagnostic to work! It took many tries but got it. The thing stopped after a minute or so and continued flashing all the dash light and never stopped.
It did however sweep the needles on all the gauges, flash a bunch of stuff and made some beeps. The odo always read or came up reading '8888888' both times I ran it.
So I guess whatever that means - there isn't an error there. What's that for? Diagnosing simply the gauges etc??

I also did verify 'P' works in dash when AT in park. And I now noticed I have a CEL active both with key in position II and with car running. It did not go away after dash self check either. Before all this started did not have a CEL on the dash. 99.5% sure of that.

My transmission switch has some wacky continuity readings. I was only able to compare all the values to a posted 2.3L 2002 Accord.
I am sort of guess they are the same 10 pin connectors and values, and if so my switch does not look right.

Key On, Engine Off, for all combos in gear.
Park, Neutral, D4, D1 all tested the same as was published and had continuity in proper combos and no continuity where it should not be.

Reverse, D2 and D3 posted bad results (All were compared to published 2002 Accord values I found).
Reverse: 3 - 9 Continuity = good value. But pin 3 -6 tested with continuity also (wrong).
D2: 2- 3 Continuity = good value. But 2 -4 Continuity tested with continuity also (wrong); 2 - 5 No continuity (bad); 5 -3 no continuity (bad).
D3: 2 -3 Continuity = good value. But 2 -5 tested with continuity (wrong); 2 - 6 No Continuity (bad); 3 - 6 No Continuity (bad).

So this is seeming to indicate bad Transmission Range Switch. I'm going to try to find a replacement and post results.

INCIDENTALLY: this connector and the cover are VERY easy to access laying next to the outside driver edge of car and going between front wheel well arch and the front tire (car not up on jack or lift). Turning wheel left all way gives a lot of nice clearance! I also strongly recommend to simply unbolt the (2) 10mm bolts that hold in the wiring harness FIRST, and then work on disconnecting the damn wire harness connector, otherwise it's near impossible for a normal person without a lift. With those out you can fish the wiring all out towards the top of engine bay and move it around to find the stupid release points. You MUST release the metal part that hold the wire in place first, then press same release point a then press the 1 large obvious button on the other side to release the green connector from the black connector. I spent several hrs on this and it could have taken minutes and a lot less swearing had I known a good cheat procedure like this. Screw the manual method.

Ohm switch. All pins infinite resistance to frame
 

I tested the switch with key on engine off.
All tens pins out of transmission range switch (aka neutral safety switch), tested Infinite resistance to the frame member motor side metal (same frame where AT grounds itself), and not reading any short or 0 or close to zero resistance on any of those pins.

DOES anyone have the 04 wiring test diagram for this exact model? It's possible the 10 pin diagram is the same for the 02 and earlier BUT it does show up as a different part when ordering.

No one stocks part in Oakland CA so I can't replace and re test for 1-3 days :confused:

Pulled the transmission range switch / neutral safety switch just now. Took it apart and lightly cleaned some dirty grease off it. But i am almost certain this isn't the problem. Switch looks good. I am totally stumped over here.

It's definitely not the transmission range switch.
Here's how I know:
I unplugged wire harness green connector from black. I powered up car with all new light bulbs in and everything else connected. Did not blow fuse #21.
However, I then jumpered pin 3 and 9 which would signal the car that it was in reverse. Result? With key in position II and switching AT through gears (car off), fuse #21 blows yet again instantly when I hit "reverse" with shifter. In Neutral and D3 and drive gears no reverse lights but dashboard gauges still working. (I start tests in neutral now always to start before putting in new fuse 21).

So SUMMARY:
Still blowing fuse #21 in reverse when everything is connected.
Transmission Range Switch not the issue
Brake pedal switch not the issue.
Found very solid grounds in tail area behind trunk plastic liner after popping out plastic fasteners. About 7-10 black wires tied in solidly there.
Also with proper green wire multi connector pulled at rear seat driver side shoulder area still blowing fuse.
Blowing fuse with old Reverse bulbs burnt out in, new bulbs in, no bulbs connected, and bulb plastic holders removed. Wiring from rear seat connector to front of car looks solid, non exposed spots anywhere in plastic loom sleeve but haven't torn that all up either.

Not really sure what else to look at now. Very stumped. MCU or MICU? PCM? TPS? Is there a neutral safety switch behind glove box?? I don't think so, it should be the transmission range switch up front.

One thing, a year ago I removed the center armrest console, passenger seat and rear bench seat, to ah, transport very large artwork and pretend I owned a minivan. Was very careful, all been working 1 year and 10,000 miles since, but is there something in that center armrest tunnel area that could cause this? I know the shift lock solenoid is there, and I have to manually press the slot to unlock the transmission when fuse #21 is blown but I think that's normal there and means solenoid is working. And if start new tests in neutral can shift and start car without pressing in solenoid bypass Anything else there??

Disassembled armrest / center console area.
Tested Shift Lock Solenoid per the Mitchell book and it tests fine.
Disconnected seat heaters, Shift Lock Solenoid and Pin lock Solenoid.
Will all bulbs in at rear of car, still blows fuse #21 instantly the second I hit reverse or row through it with the shifter.

I have really no idea how to solve this and it continues to be a big problem.

Here's the Transmission Range Switch as I metered it with my ohm Meter.
It is different from the published 2002 2.3L Accord diagram I found.
Does this look wrong and a problem?

ESPECIALLY reverse circuit? Should it only have continuity between #3 and #9 pins and not also #3 to #6 pins, and #9 to #6 pins? Is that an issue and causing a short and blowing my fuse?
In my drawn diagram of continuity findings, the left √ checked column mean it was the same as 2002 2.3L Accord diagram. X means it was different.
So D3 and D2 did not have continuity with pins 6 and 5 respectively as the 2002 Accord has, but rather had continuity with pins 5 and 4 respectively.

The reason I think it isn't is the switch looked fine taken apart
and I was thinking I also shifted into reverse and still blew the fuse with Switch totally disconnected, but now I am wondering if I remembered that wrong? Can you shift car with that out? I think you can and I did, but I think main thing is I can't start the car and I cannot remove the key with it unplugged (which makes sense).

2nd pic is diagram I found for the Transmission Range Switch on the 2002 Accord 2.3L I understand these are different part #s to replace.

This is a very odd one and I'm at my wits end....almost. So however this ends up PLEASE let us know how it ends up.

So here I go with some "wild" ideas.

Can you start the car, set the e-brake. Use the shift lock release and try to shift the car thru R to D4?

Next, that fuse also goes to the comb light switch......start the car and run the headlights thru all of the functions - park, headlight, high beams, left right turn signals?

I will absolutely post the fix to whatever this is.
Today I've resorted all day to manually unlocking transmission (even easier now with center armrest console gutted), and shifting in neutral with parking brake cranked on. I then put in fuse #21, THEN I start the car, and remember to never shift into reverse (or through to park either), before I pull over and stop, crank E Brake, put in Neutral, and pull fuse again.

I can easily shift into any gear manually releasing shift lock - or with a working #21 fuse provided I don't touch reverse. I can shift car off, or car running. All gears are easy to go into, and correct and show up on shifter and dash (if I do the above tricks) as correct numbers.
I do have a small bit of concern about the Transmission Range Switch graph I metered and made compared to the 2002 version - it's quite different.
I also noticed today that twice using my trick above to have gauges and most importantly P. Windows (!) working that the passenger airbag light came on and went off at a random time driving - I know that indicator is in circuit #21 but at that time, the circuit was alive and working fine (had been avoiding reverse with new fuse in). There was also a passenger with me in the seat. My previously seen CEL is nowhere to be seen today.

With or without fuse #21 circuit ok or blown, I can cycle headlights through everything just fine, low beams, high beams and fog lights all work. Hazards all work too. But if fuse #21 is blown, then my blinkers at that point won't work at all, but headlights still works fine in hi / low etc...

I guess since I keep blowing the fuse if I have a working fuse in slot #21, it means I either have a shorted component (and I think I've pulled them all and verified they all work on the reverse circuit except for the MICU), or more likely a shorted 12V live wire, not a bad ground.
Have not metered from Transmission Range Switch connector harness to the fusebox, nor from the fusebox to the Shift Lock Solenoid or the Pin Lock Solenoid connectors, nor from the fusebox to the rear seat driver side shoulder area connector yet. I guess that's all that can be done next or throw money at a MICU which means replace entire fusebox ?
?
Thanks for your continued help and ideas!

Unplug the transmission range switch and use a piece of wire to jump the white wire to the black wire. Turn the key to the II position (or what you normally do to blow that fuse) and see if the #21 fuse blows.

That yellow wire that causes the fuse to blow goes into the gauge control module, which is part of the instrument cluster. You may want to inspect the circuit board of the cluster to see if there are signs of damage.

Sadly it's goin to be at least ten days before I am back home to car now on a flight to Alabama!
I will try the yellow lines and such and disconnecting the Trans switch and post back what I find next.

Back at car. I feel like I am about to kick this car off a cliff or f-ing rewire the whole damn car myself.
Needless to say, nothing I try is working.
I put in a replacement Transmission Range Switch today and it instantly blew fuse #21 in reverse again.
I can ONLY get the car now to actually go into reverse and not blow the fuse in one way:
I disconnected a major wire connector under I think it's the TPS in the engine bay. Its probably a 20 or 24 pin connector and i could snap a pic but my gf took the crippled car. This is a four connectors plugin area about 3/4 to the back of engine bay up relatively high behind the motor. It was the one carrying the green wire with grey dots painted on it that eventually makes its way after several split offs to the transmission range switch.

By the way, I've tested for continuity and got it on every wire from the transmission range switch connector and up to the connector that disconnects a ways above the transmission.

I've disconnected so many things in the car - everything in the back trunk area at the four way connections at the rear seat drive side, all connectors in the shifter area (shift lock solenoid, cigarette lighter, heated seats, pin lock solenoid, etc...), disconnected connections around the center console and even the green wire connection at the ECM or ECT there and nothing will prevent blowing fuse #21 when I shift into reverse except for the above mentioned engine bay connector. I was excited I thought that almost certainly meant the Trans Range Switch was bad (shorting itself) and when replaced it, it did nothing to fix.
Visually all engine wiring looks fine. Nothing has been modified or replaced in there except for dealer service over 1.5 years back.
I tested the green wiring in the trunk area for continuity end to end and got continuity there.
I don't know where wires connect to where in the engine bay or what this could or could not mean. I don't even know if a wire will show Zero resistance (continuity) if it's shorted. I would think not, right?

Disconnected transmission range switch and jumpered black and white wires and put key in "II" position and fuse blew again. This was as expected. I am sure switch is fine.
I found some good wiring diagrams today but not quite sure how to interpret them, there are tons of diagrams and still not sure where to look next.

ONLY way shifter can go into reverse and not blow fuse #21.
 

As pictured below - this is currently the ONLY way I can put car in reverse with AT shifter and not blow fuse #21. I have to disconnect this connector - the one pointed to - it's the upper connector of the two there.
It may be meaningless or insignificant. (?)

Does that fuse also feed the back-up lights? That looks like the trans position sensor, so how about a short in the circuit for the backup lights? (Its a long thread so maybe you've already ruled that out)

It most likely is a short in the circuit. That connector looks to be the junction connector C201 (a 33-P connector). The short may between that harness connector and connector C152. Check the Wht or Wht/Grn wire along that circuit.

Thanks for the responses!
Yes Jim, it is on that circuit for back up light (fuse #21), the Trans Switch wires up to it.
So there is some sort of a short somewhere.
I'm going to look at the pics and info in post 2 now.

edit:
So Connector "C 152" is the connector I've removed 2x and at the switch. That cluster of wires has continuity on each wire from C 152 end to the Trans Range Sw end.
(not sure if there can still be a problem. but they all have continuity, and looked fine. Connector pins all look normal / clean no black etc...). Trans Range Sw. is good. And, yes, it was C 201 I disconnected and then I can shift car trans in reverse without blowing the fuse, that's the only way I've found. So should I examine (how?) the wires from C 152 to C 201? And / or from C 201 on? Or, wait, I guess it can't be beyond that right... or can it, if the 12V gets returned from the Trans Range Sw back to indicate it's in reverse and activate back up lights, could it then be anywhere else upstream too? (?)

edit the edit:
Ok, RedBull, much thanks, after re-reading and studying all your attached pics, I think you're right, look between C 152 and C 201 for the short by looking at White/Green wire. Soo... should I pull apart the wire protector or try to run voltage up that wire - disconnected at both ends with a 12VDC test lamp in between that and the positive on my small extra 12VDC battery and the negative terminal? Is that a way to do this?

I have a small 12V DC battery for running a light. Should I shoot some of that up a wire to try to see if there's a short? Is checking for continuity enough to verify a wire is solid and not shorting? I'm a mostly new to this part, and online posts usually gloss over those details of how to actually check for shorts besides disconnecting things and narrowing it down.